In radiometery, thermal radiation sensors are used to detect radiant infrared energy. A typical example of such sensors are thermopiles which generally consist of a multiplicity of thermocouples connected in series. Each thermocouple is made of a pair of unlike materials connected at two points, one point being a hot junction and the other being a cold junction. When the junctions are at different temperatures, an electromotive force is developed across the thermocouple. In a typical thermopile, the hot junctions are located in an absorber area of the thermopile, and the cold junctions are located at an outer rim region. Most thermopiles are made as a planar array supported on a film which in turn is supported by the outer rim. These framed structures are usually held within a hermetic enclosure to prevent undesirable gases from entering and/or to seal in a desired gas. The enclosure also has a window to permit radiation to pass through the enclosure and impinge upon the absorber area of the thermopile. Although lead wires extend from the thermopile planar array through the enclosure, the feedthroughs for the lead wires are also hermetically sealed, that is, gases cannot penetrate the passageway through which the lead wires extend.
The typical thermopile planar array is very delicate and can be easily damaged when handled, for example, during fabrication of the sensor. Thus placing the thermopile in the enclosure is both laborious to the assembler and hazardous to the thermopile. As such, it is desirable to fabricate the enclosure, or at least a portion of the enclosure, along with the thermopile to increase cost savings by using less labor and generating a larger yield of thermopiles.
The present invention implements a radiation sensor which includes a thermopile for detecting radiant energy. The thermopile and a support rim for the thermopile are fabricated as an integrated unit to form a support chip. The support chip is mated to a mating chip so that the thermopile is positioned in an inner cavity region of the radiation sensor. The sensor has a window which permits the transmission of radiant energy into the enclosure such that the radiant energy impinges upon a central absorber region of the thermopile.
In one aspect of the invention, the sensor includes a support chip having an outer rim and a thermopile supported by the rim. The sensor also includes a mating chip having a rim region and a window region. The rim region of the mating chip is mated to the outer rim of the support chip to form a hermetically sealed enclosure in which the thermopile resides.
Embodiments of this aspect can include one or more of the following features. The thermopile includes a plurality of thermocouples connected in series and an inner absorber region. A hot junction of each thermocouple is positioned in this inner absorber region, and a cold junction of each thermocouple is positioned in the rim regions of the support chip and the mating chip. The thermocouples can be made from bismuth and antimony, or from other suitable materials such as, for example, chromel, alumel, and constantan, as well as semiconductor materials, such as P-type silicon.
A cap of the support chip and the outer rim can be made from a common semiconductor wafer, for example, silicon, and the materials of the thermopile can be deposited on this wafer. The mating chip can be made from another wafer. Alternatively, the outer rim can be made from one wafer, with the materials of the thermopile deposited on this wafer, and a window layer can be made from another wafer, with the window layer being mated to a one side of the support chip. The mating chip can be made from a third wafer such that it is mated to the other side of the support chip.
In some embodiments, the radiant energy which impinges on the inner absorber region of the thermopile can have a wavelength that ranges from about 1 xcexcm to about 14 xcexcm.
The thermopile can have at least two leads which are attached to a respective terminal positioned on an exterior surface of the sensor. Each terminal can be positioned in a respective etch pit of the support chip, or the terminals can lie in the same plane as the thermopile in a common etch pit. The sensor can also include a reference terminal positioned on the exterior surface.